The critical role of stereochemically active lone pair in introducing high temperature ferroelectricity

TL;DR

This study demonstrates that stereochemically active lone pairs, particularly from Pb2+, induce structural distortions leading to room temperature ferroelectricity in langasite compounds, unlike their non-lone pair counterparts.

Contribution

It provides a comparative analysis showing how lone pair activity from Pb2+ induces ferroelectricity in langasite structures, a novel insight into designing high-temperature ferroelectric materials.

Findings

Pb3TeCo3P2O14 exhibits room temperature ferroelectricity.

Structural distortion is driven by stereochemically active lone pairs.

Lone pair activity influences the polar geometry formation.

Abstract

In this paper a comparative structural, dielectric and magnetic study of two langasite compounds Ba$_3$TeCo$_3$P$_2$O$_{14}$ (absence of lone pair) and Pb$_3$TeCo$_3$P$_2$O$_{14}$ (Pb$^{2+}$ 6$s^2$ lone pair) have been carried out to precisely explore the development of room temperature spontaneous polarization in presence of stereochemically active lone pair. In case of Pb$_3$TeCo$_3$P$_2$O$_{14}$, mixing of both Pb 6$s$ with Pb 6$p$ and O 2$p$ help the lone pair to be stereochemically active. This stereochemically active lone pair brings a large structural distortion within the unit cell and creates a polar geometry, while Ba$_3$TeCo$_3$P$_2$O$_{14}$ compound remains in a nonpolar structure due to the absence of any such effect. Consequently, polarization measurement under varying electric field confirms room temperature ferroelectricity for Pb$_3$TeCo$_3$P$_2$O$_{14}$, which was not the case of Ba$_3$TeCo$_3$P$_2$O$_{14}$. Detailed study was carried out to understand the microscopic mechanism of ferroelectricity which revealed the exciting underlying activity of poler TeO$_6$ octahedral unit as well as Pb-hexagon.